This invention relates to a system, for installation on board an aircraft, for detecting either a locked wheel or a binding wheel, and for advising the operators of the aircraft of these conditions. The system is effective during taxi-out and during the take-off roll to detect a locked wheel; and is effective immediately after lift-off to detect the abnormally high deceleration rate of a binding wheel.
The main landing gear of aircraft may consist of as few as two wheels having inflated tires, or modern high capacity aircraft may include as many as eight or twelve or sixteen such wheels; and these landing gear structures are capable of withstanding enormous loads and shocks at very high landing and take-off speeds.
For such aircraft there is no practical system known which advises the operators within the aircraft of the wheel or brake condition. In an aircraft having a large number of main gear wheels, one wheel may be fully locked and this would not necessarily be noticeable to the operators, on the take-off or landing roll for example, until a resulting more serious situation is created. If one wheel is locked or nearly locked, for example, the tire will likely blowout fairly soon; and this creates a higher load on the adjacent tires encouraging further tire failures in the manner of a chain reaction. It is most desirable that the aircraft operators be advised of a locked wheel or a particular locked wheel as soon as possible, so that appropriate corrective action may be taken.
If one wheel is locked or nearly fully locked at the time of landing of the aircraft, unknown to the operators, severe damage to that wheel and its associated support structure will certainly be sustained. More seriously the loss of that one wheel may cause loss of control of the aircraft on landing or may induce a chain reaction of further wheel losses which are extremely hazardous to the safety of the aircraft and its cargo or passenger load. For an aircraft having a smaller number of landing gear wheels, the loss of one wheel is much more hazardous than that for an aircraft with a larger number of wheels.
One form of system which has been employed for detecting brake failure, is a thermocouple system for detecting heat buildup in wheels and potential brake failure due to overheating. Such a system has been found defective because it does not indicate the problem until the brake lockup is imminent. The system is unreliable because it depends on relatively fragile wire conductors which are susceptible to damage during normal wheel maintenance operations, and which wires are frequently disconnected during normal wheel maintenance changes, etc. resulting in possible inadvertent failure to reconnect.
A principal object of this invention is to improve the safety of aircraft operation.
Another principal object of this invention is to provide an effective and reliable system to enable detection, by the aircraft operating personnel, of a locked wheel before the aircraft leaves the ground, or of a binding wheel immediately after lift-off, so that appropriate action may be taken to prevent or minimize damage or accident.
Another object of this invention is to provide such a system which will detect a binding wheel independently of any of the other wheels of the aircraft and without necessity for comparison with another wheel.
A further object of this invention is to provide such a system which enables detection of a locked wheel during the taxi-out of the aircraft, and in which the operation of the system during taxi-out functions simultaneously as a check on the operativeness of the system particularly with respect to the indicator lights.
Still another object of this invention is to provide such a system which enables detection of a binding wheel by detecting abnormal deceleration of the wheel immediately after lift-off, whereby the aircraft operator is forewarned of this condition enabling precautionary measures on the subsequent landing of the aircraft.
A still further object of this invention is to provide such a system for use complementary to a brake anti-skid system, with the two systems utilizing the output from the same wheel speed transducer.
Another object of this invention is to provide such a system which monitors wheel condition continuously during frequent taxi stops and starts in heavy traffic.
Certain of these objects are accomplished in a system which includes a signal generating means, including a wheel speed transducer means coupled to one wheel, for producing a DC voltage wheel speed signal which is proportional to the rotational speed of that wheel. An electrically operated indicator indicates one of two conditions.
A comparator circuit compares DC voltage wheel input and reference input signals, and produces an output signal when the wheel input signal goes negative relative to the reference input signal. A first charging circuit couples the output of the signal generating means to one comparator circuit input for producing said wheel input signal which tracks the increasing and decreasing wheel speed signal. A second charging circuit couples the output of the signal generating means to another comparator circuit input for producing said reference input signal which tracks the increasing wheel speed signal at a selected lower value whereby the reference input signal is maintained negative relative to said wheel input signal during the tracking of an increasing wheel speed signal, and which reference input signal tracks the decreasing wheel speed signal with a time delay greater than that of said wheel input signal whereby said wheel input signal will go negative relative to said reference input signal for an abnormally high deceleration rate of said wheel. The comparator circuit output is coupled to the indicator.
For accomplishing other objects, a second comparator compares two DC voltage input signals and produces an output signal for energizing said indicator when one input is positive relative to the other. The comparator circuit includes means producing a fixed, threshold voltage signal. A charging circuit couples the output of the signal generating means to the other input of the second comparator for producing a DC voltage on-ground input signal which tracks the increasing and decreasing wheel speed signal, and effects shutoff of the comparator output when the on-ground input signal goes positive relative to the threshold signal, thereby de-energizing the indicator means.